This invention relates to a pressure-elevating type fuel injecting system in which high pressure fuel from a pressure accumulating chamber is further pressurized by a pressure elevating mechanism and is injected into combustion chambers via injectors, and more particularly to a pressure-elevating type fuel injecting system which can precisely inject fuel to cope with a load in accordance with an operating state of an internal combustion engine.
A pressure-elevating type fuel injecting system is one of fuel injecting systems which inject fuel to combustion chambers of an internal combustion engine via injectors. In such a pressure-elevating type fuel injecting system, high pressure fuel from a fuel supply is stored in a pressure accumulating chamber constituted by a common rail, and injector nozzles coupled to the common rail face with the combustion chambers. Further, a pressure elevating mechanism is disposed in a branch of a high pressure fuel supply path extending between the common rail and the injectors. In the pressure-elevating mechanism, a power piston is actuated by pressure of the high pressure fuel applied via the branch of the high pressure fuel path, and feeds the pressurized fuel to the injectors. In short, the power piston is operated by a pressure elevating piston electromagnetic valve. For instance, the pressure-elevating type fuel injecting system operates as shown in FIG. 5 of the accompanying drawings. Specifically, fuel injection is started when a signal n1 for actuating an injector electromagnetic valve is issued at a timing t01. Pressure Pc at the common rail is elevated when a signal n2 for actuating the pressure-elevating piston electromagnetic valve (called the xe2x80x9cpiston electromagnetic valvexe2x80x9d) is issued at a timing t02. Further, the pressurized fuel has a time-dependent pressure variation as shown by Ph, and is injected with a fuel injection ratio pm.
Fuel injection is carried out in two steps. Specifically, an initial fuel injection j1 is performed between the timing t01 (at which the injector electromagnetic valve is opened) and the timing t02 (at which the piston electromagnetic valve is opened), and a final fuel injection j2 is performed between the timing t02 and a timing t03 at which the injector electromagnetic valve is closed. This measure has been taken in order to reduce exhaust gases and engine noise.
In an ordinary common rail type fuel injecting system, an injection pressure usually corresponds to a common rail pressure. Therefore, an injector operating period corresponding to target fuel injection quantity is determined on the basis of the common rail pressure which is monitored immediately before the fuel injection, in place of the injection pressure.
However, with the pressure-elevating type fuel injecting system, an injection pressure of pressurized fuel does not correspond to the common rail pressure. In other words, the common rail pressure cannot be applied as the injection pressure. Therefore, the injection pressure has to be separately monitored.
In the foregoing case, a sensor should be provided at a nozzle hole of each injector in order to detect the injection pressure. However, it is very difficult to secure sensor spaces in the injectors. Further, the sensors have to be provided in all of the injectors, which is not advantageous in view of cost.
If the injection pressure is not monitored, it is impossible to determine operation periods of the injectors and piston electromagnetic valves on the basis of the common rail pressure which varies with operating states of the engine, the operation period of the pressurizing piston, and so on. Therefore, it is very difficult to precisely control the fuel injection and stabilize the engine control.
The present invention has been contemplated in order to overcome the foregoing problems and to provide a pressure-elevating type fuel injecting system in which fuel injection is precisely controlled in order to stabilize engine operations.
A pressurized fuel injecting system in which high pressure fuel from a pressure accumulating chamber is further pressurized by a pressure elevating mechanism and is injected into combustion chambers by injectors. The pressure-elevating type fuel injecting system comprises: a target fuel injection quantity setting unit which sets a target fuel injection quantity in accordance with an operating state of an engine operation; a time difference setting unit which sets a time difference between a timing for opening an injector electromagnetic valve enabling fuel injection or no-fuel injection from injectors, and a timing for opening an pressure-elevating mechanism electromagnetic valve turning on or off the pressure-elevating mechanism; an initial injection quantity calculating unit which calculates an initial fuel injection quantity on the basis of a time-dependent variation of fuel pressure during the opening of the pressure-elevating mechanism electromagnetic valve and the time difference derived by the time difference setting unit; and a final injection period setting unit which calculates an opening period of the injector electromagnetic valve, on the basis of a final fuel injection quantity derived by deducting the initial fuel injection quantity from the target fuel injection quantity, and the time-dependent variation of the pressure of the pressurized fuel during the opening of the pressure-elevating mechanism electromagnetic valve.
The initial injection quantity calculating unit calculates the initial fuel injection quantity on the basis of the time-dependent variation of the fuel pressure and the time difference calculated by the time difference setting unit. The final injection period setting unit calculates the final injection period on the basis of the final injection quantity derived by deducting the initial injection quantity from the target injection quantity, and the time-dependent variation of the fuel pressure. Therefore, it is not necessary to monitor the fuel pressure near nozzle holes of the injectors. Further, the fuel injection can be precisely controlled, and reliable and stable operation of the engine can be assured.
Further, the initial injection quantity calculating unit calculates the initial fuel injection quantity on the basis of the time-dependent variation of the fuel pressure during the opening of the pressure-elevating mechanism electromagnetic valve, the time difference, and fuel pressure in the pressure accumulating chamber. The initial fuel injection quantity is increased in response to an increase of the fuel pressure in the pressure accumulating chamber. The initial injection quantity can be precisely determined, so that the fuel injection can be appropriately controlled, and reliable and stable operation of the engine can be assured.
Still further, the final injection period setting unit calculates the final fuel injection period on the basis of the time-dependent pressure variation of the pressurized fuel during the opening of the pressure-elevating mechanism electromagnetic valve. The final fuel injection period is shortened in response to an increase of the fuel pressure in the pressure accumulating chamber. The final fuel injection quantity can be precisely determined, so that the fuel injection can be appropriately controlled, and reliable and stable operation of the engine can be assured.